1. Field of the Invention
The present invention relates to an organic electroluminescence device. In particular, the invention relates to an organic electroluminescence device with a reduced lateral current leakage.
2. Descriptions of the Related Art
Since organic electroluminescence devices with high brightness had been developed by Tang etc. in 1987, organic electroluminescence devices for use in displays has caught a lot of attention. Various researches and developments have been successively carried out in industries and academies.
FIG. 1 is a schematic view illustrating a conventional organic light emitting diode (OLED) display 1 which comprises a plurality of pixel areas 10. On each pixel area 10, a thin-film-transistor (TFT) 11 and an organic electroluminescence device 13 are disposed. Furthermore, a plurality of scan lines 15 and data lines 17 are utilized to control the display 1.
FIG. 2 illustrates a cross-sectional view of each pixel area 10. When voltages applied from the scan lines 15 turn on the TFT 11, the organic electroluminescence device 13 will be subsequently driven to emit light through a transparent electrode 21 and an organic electroluminescence unit 30 on a luminescence area 131.
FIG. 3 is an enlarged view illustrating the organic electroluminescence device 13 within the broken circle as shown in FIG. 2. The organic electroluminescence device 13 comprises the transparent electrode 21 (acting as an anode), the organic electroluminescence unit 30, and a common electrode 23 (acting as a cathode). The organic electroluminescence unit 30 successively comprises a hole-injecting layer (HIL) 31, a hole-transporting layer (HTL) 32, a light-emitting layer 33, an electron-transporting layer (ETL) 34, and an electron-injecting layer (EIL) 35. In accordance with practical applications and material selections, the HIL 31, the HTL 32, the ETL 34, and the EIL 35 can be combined into a single layer, separately disposed, or alternatively not disposed in the organic electroluminescence unit 30. When specific voltages or currents are applied between the electrodes, the electron current generated from the common electrode 23 and the hole current generated from the transparent electrode 21 flow into the device. Subsequently, the electrons and the holes are both transmitted into the light-emitting layer 33 and then combined into excitons for emitting light.
Specifically, when a bias is added, the electrons and holes transmit into the light-emitting layer 33 through the ETL 34 and the HTL 32, respectively. The light-emitting layer 33 is formed by organic electroluminescent materials. After the electrons and holes combine into excitons, they turn to ground state with light emission. According to the selections of the luminescent materials and the spin state characteristics of the electrons, lights will be emitted with different colors.
In general, the conventional HIL 31 is made of hole-transporting materials doped with high concentration of P-type substances. This can improve the thermal stability of the device and enhance its hole-injecting characteristics or conductivity, so as to reduce the working voltage of the device. Although this structure can significantly enhance the hole-injecting and hole-transporting abilities of the device, it also results in lateral current leakage due to high lateral conductivities. Thus, the working efficiency of the device is also reduced.
Referring to FIGS. 2 and 3, the organic electroluminescence device 13 is generally expected to respond merely in the luminescence area 131 for displaying. However, the final products will emit light on area 132 as well due to the aforementioned lateral current leakage. This will cause serious, undesired light leakages in OLED displays.
Accordingly, it is desirable to provide an organic electroluminescence device with a reduced lateral current leakage.